Study of ion beam and neutral beam characteristics through particle simulation

Abstract

Ion beam generation scheme using an acceleration grid system has many different applications. In the material processing area, the application includes plasma implantation, reactive ion etching, and neutral beam generation. One of the main issues in the ion beam generation has been in the raising of the beam flux. The research has been confined to the grid hole diameter, the grid gap, the grid voltage distribution, and the source plasma density. Even though a considerable progress has been made in optimizing these physical conditions, a higher ion beam flux is still in demand without warrant for further improvement. A different approach and the fundamental physics understanding may now be needed for further advances in this field. In the present research, an uncommon computational approach is taken to understand the physics and to examine the possibility of raising the ion beam flux by applying a voltage bias on the conducting wall of a numerical plasma source. The simulation performed here is uncommon in the sense that the source plasma, sheath potential and the acceleration grid hole are considered in a self-consistent manner. It is found that a strongly positive wall-biasing can significantly enhance the ion flux by improving the shape of the plasma sheath potential meniscus at the entrance to the grid hole structure. It is also found that a weak positive wall-biasing can actually reduce the ion flux by distorting the plasma sheath potential meniscus without improving the overall shape. A neutral beam source is one of candidate methods to reduce plasma-induced damage problems. The ion beams extracted through the grid structure are directed to the surface of a conducting plate (reflector) and are converted into neutral beams. A molecular dynamics simulation tool has also been developed using a molecular dynamics algorithm. The roughness of the reflector surface is experimentally measured and taken into consideration in the simulation. The energy and angular...